Japanese unexamined utility model application publication No. JP-UM-A-5-96857 (hereinafter, Patent Document 1) and Japanese unexamined patent application publication No. JP-A-2000-219382 (hereinafter, Patent Document 2) describe related art image forming apparatuses. The related art image forming apparatus described in Patent Document 1 includes a conveyance unit which conveys each sheet along a conveyance path; and an image forming unit such as a photoconductive drum, a transfer unit, etc. which forms an image on the sheet while the sheet is conveyed by the conveyance unit. A feed roller and a sheet guide are provided in the conveyance path. The feed roller conveys the sheet. The sheet guide is located on a downstream side of the feed roller with respect to a sheet conveyance direction. The sheet guide guides the sheet to the conveyance path.
The related art image forming apparatus described in Patent Document 2 is configured so that each sheet is guided by a guide plate in a turn portion which changes a conveyance direction in the middle of conveyance of the sheet.
When a firm thick sheet is used in the related art image forming apparatus described in the Patent Document 1, collision noise sometimes occurs because a trailing end of the sheet bounces due to an elastic force of the sheet as the sheet suddenly collides with the sheet guide after the trailing end of the sheet passes through the feed roller. The term “trailing end of the sheet” denotes an end portion of the sheet which is located on a rear or downstream side with respect to the sheet conveyance direction when the sheet is conveyed along the conveyance path.
In order to reduce the collision noise, Patent Document 1 provides a shock absorbing unit between the feed roller and the photoconductive drum. The shock absorbing unit absorbs shock when the sheet passes through the feed roller. The shock absorbing unit is rotatably supported on a rotary shaft of the feed roller. When the trailing end of the sheet passes through the feed roller, the shock absorbing unit presses the trailing end portion of the sheet downward using only the weight of the shock absorbing unit itself. Then, the trailing end of the sheet thus presses against the shock absorbing unit providing a counterforce against the weight of the shock absorbing unit so as to rotate the shock absorbing unit upward. Accordingly, the upward rotation of the shock absorbing unit cancels the elastic force by which the trailing end of the sheet is bounced up. As a result, the trailing end of the sheet can be prevented from being bounced up suddenly, so that the trailing end of the sheet can be restrained from colliding with the sheet guide.
However, the above collision noise caused by collision of the sheet bouncing in the conveyance path is not limited to the location described in Patent Document 1. For example, in a related art image forming apparatus, a feed tray on which sheets are received is provided so as to be detachably attached to a main body of the apparatus. Each sheet is received by the conveyance path of the body from the feed tray. Accordingly, a difference in level is provided between the feed tray and the conveyance path in order to prevent the conveyance path from blocking a leading end of the sheet that is conveyed to the conveyance path from the feed tray. In this configuration, collision noise is caused by collision of the sheet with the conveyance path on the main body when the sheet passes through the level difference portion. This level difference portion is also sometimes referred to as a step portion between the feed tray and the conveyance path.
To prevent such collision noise in the step portion, for example, Patent Document 2 describes a related art image forming apparatus having configuration in which the step portion of the guide plate is inclined with respect to the widthwise direction of the sheet. However, in Patent Document 2, a roller is provided in the middle of the guide plate, and a level difference is formed between the roller and the guide plate. Accordingly, there is a case in which collision noise is caused by collision of the sheet with the guide plate when the sheet passes through the roller.